There are a lot of folks who go to church for years believing that they have a relationship with God, because they believe He exists. They view their faith in the Creator revealed in the Bible as indicating that they are saved. After all, the Bible says that whoever acknowledges Jesus as Lord is a Christian, right? They attend Bible conferences, music festivals, tithe, visit the sick, and even weep when they hear the testimonies of others; of course they are saved, right?
Let's take each question one at a time. Does believing God exists save you? "Thou believest that there is one God; thou doest well. The devils (demons) also believe, and tremble" (Jam. 2:19). The context of this verse is that James needed to see evidence that a person was saved before he would accept his testimony (Jam. 2:14-26). According to James, a genuine believer shows evidence that he is saved in two ways: one, he helps those in need (v. 14-19); and two, he obeys God's will (v. 21-26). Notice that James didn't say anything about going to church, or about understanding doctrine. The Pharisees believed in the God of the Bible, they "religiously" attended every "worship service" required by Old Testament doctrine, and they gave tithes, offerings, and even alms to the poor. And yet, they did not recognize their Savior or their need to be born again (Jn. 3:1-9).
What about those who call Jesus Lord? Well, it depends on how you define the word "Lord." If you define it as presented in the Old Testament, you must choose between a person worthy of respect or God. In 1 Kings 1:17, both uses of the word are given and the difference in meaning is obvious: "And she said unto him, 'My Lord, thou didst swear by the LORD, thy God...." One is acknowledging the superiority of the person, and the other is a replacement for the name of God because the Jews were afraid to speak His name. While the New Testament does not use "LORD," it is clear that those using the word when addressing Jesus had the wrong understanding of Who He was. In Matthew 7:21-23, Jesus teaches that there is a difference in someone saying "Lord" out of respect, and one who recognizes that Jesus is the Lord Who deserves obedience. In this example, those to whom He was speaking had done good works in His name, but they were doing them in order to "qualify" for heaven. They were not doing what God wanted; they were religious but had no relationship with God, and therefore did not know what He wanted them to do.
To sum up, a person who has accepted Jesus as Lord will do good works out of gratitude for what He has done for us on the cross (Eph. 2:10). And the works he does are only those works that God has personally shown him to do (Jn. 14:15). When Jesus is Lord, the works we do out of gratitude and obedience reveal our relationship with Christ, and result in God getting the glory. Jesus is LORD, not just Lord!